Why haven’t we encountered aliens yet? The answer could be climate change

The Fermi Paradox has been increasingly questioned, but there are no answers yet.

Enrico Fermi, when asked about intelligent life on other planets, famously replied, “Where are they?” Any civilization advanced enough to undertake interstellar travel would, he argued, in a brief period of cosmic time, populate its entire galaxy. Yet, we haven’t made any contact with such life. This has become the famous "Fermi Paradox.”

Various explanations for why we don’t see aliens have been proposed—perhaps interstellar travel is impossible or maybe civilizations are always self-destructive. But with every new discovery of a potentially habitable planet, the Fermi Paradox becomes increasingly mysterious. There could be hundreds of millions of potentially habitable worlds in the Milky Way alone.

This impression is only reinforced by the recent discovery of a “Mega-Earth," a rocky planet 17 times more massive than the Earth but with only a thin atmosphere. Previously, it was thought that worlds this large would hold onto an atmosphere so thick that their surfaces would experience uninhabitable temperatures and pressures. But if this isn’t true, there is a whole new category of potentially habitable real estate in the cosmos.

Finding ET

So why don’t we see advanced civilizations swarming across the Universe? One problem may be climate change. It is not that advanced civilizations always destroy themselves by over-heating their biospheres (although that is a possibility). Instead, because stars become brighter as they age, most planets with an initially life-friendly climate will become uninhabitably hot long before intelligent life emerges.

Further Reading

The Earth has had four billion years of good weather despite our Sun burning a lot more fuel than when Earth was formed. We can estimate the amount of warming this should have produced thanks to the scientific effort to predict the consequences of man-made greenhouse-gas emissions.

These models predict that our planet should warm by a few degrees centigrade for each percentage increase in heating at Earth’s surface. This is roughly the increased heating produced by carbon dioxide at the levels expected for the end of the 21st century. (Incidentally, that is where the IPCC prediction of global warming of around three degrees Celsius comes from.)

Over the past half-billion years, a time period for which we have reasonable records of Earth’s climate, the Sun’s surface temperature increased by four percent, and terrestrial temperatures should have risen by roughly 10 degrees Celsius. But the geological record shows that, if anything, on average temperatures fell.

Simple extrapolations show that over the whole history of life, temperatures should have risen by almost 100 degrees Celsius. If that were true, early life must have emerged upon a completely frozen planet. Yet, the young Earth had liquid water on its surface. So what’s going on?

Get lucky

The answer is that it's not only the Sun that has changed. The Earth also evolved, with the appearance of land plants around 400 million years ago changing atmospheric composition and the amount of heat Earth reflects back into space. There has also been geological change with the continental area steadily growing through time as volcanic activity added to the land-mass. This too had an effect on the atmosphere and Earth’s reflectivity.

Remarkably, biological and geological evolution have generally produced cooling, and this has compensated for the warming effect of our aging Sun. There have been times when compensation was too slow or too fast, and the Earth warmed or cooled, but not once since life first emerged has liquid water completely disappeared from the surface.

Our planet has therefore miraculously moderated climate change for four billion years. This observation led to the development of the Gaia hypothesis that a complex biosphere automatically regulates the environment in its own interests. However, Gaia lacks a credible mechanism and has probably confused cause and effect: a reasonably stable environment is a precondition for a complex biosphere, not the other way around.

Other inhabited planets in the Universe must also have found ways to prevent global warming. Watery worlds suitable for life will have climates that, like the Earth, are highly sensitive to changing circumstances. The repeated canceling of star-induced warming by “geobiological” cooling, required to keep such planets habitable, will have needed many coincidences, and the vast majority of such planets will have run out of luck long before sentient beings evolved.

However, the Universe is immense, and a few rare worlds will have had the necessary good fortune. It may just be that Earth is one of those lucky planets—a precious, fragile jewel in space. So, perhaps inevitably, climate change will remain a bane of the continued existence of life on such planets.

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356 Reader Comments

We need to make great effort to speak with the Voyager spacecraft who we know how to speak to. WTF do we think alien noise might be? Why would they put massive energy into something to speak to others? Just to put it out there? A billion watt beacon? Something the energy of quasars, so we could say we aren't alone in the universe. An intelligent being would use low watt communication, why use more than required? With hundreds to thousands of years between systems (without faster than light travel), efforts are great to just go visit random systems. Fermi paradox is an idea, easily dismissed.

Yup, it's climate change. When aliens hear Republicans talking about it, they realize that if humans can't come to grips with basic science, they aren't going to be able to handle something like alien contact!

or just maybe the universe is so big that any aliens intelligent enough to build a spaceship that can travel interstellar distances tries to avoid the hassle of bumping into primitive complications. After all it's not like the universe is lacking in alternative solar systems and planets to colonise. At most we might be an interesting anthropological study for some university project in a galaxy far far away…

A billion watt beacon? Something the energy of quasars, so we could say we aren't alone in the universe. An intelligent being would use low watt communication, why use more than required?

An intelligent being with only slightly more resources than us would float a big statite between the Sun and the target, and modulate the sun's output. A big-ass (a few hundred km across) Mylar solar sail with rotatable 'panels' and a DC-free coding scheme (equal number of ones and zeroes, to ease stationkeeping) would give you a low-bitrate high signal-to-noise output.

Any society complex enough to produce interstellar travel is also complex enough to produce automation and flawless simulation; thus obviating the immediate need for said interstellar travel. The galaxy would be colonized slowly, if at all.

Right. I would also assume that a society *that advanced would have already solved all of its domestic problems, and have economies many times the sophistication and breadth of our countries. Why would they want to endure the enormous financial pressure of colonizing other systems, when everything is just about perfect at home?

I disagree, I think a society advanced enough to be able to travel the stars would try to colonize at least a few other planets near other stars simply to increase the chance of the survival of their species. Remember that unpredictable things do happen - massive gamma rays or solar storms etc. Catastrophic events which are seemingly random can happen and just having a few more islands of life a species would increase their chance of survival by spreading out.

Interstellar travel is essentially impossible, at least at our current understanding of physics and level of technology. Even if it is technically possible to cross the distance between star systems, the cost from an energy standpoint would be staggering - just think about how much energy it takes to move a kilogram of weight to orbit, and how much more to send it out of the solar system.

My best guess is that the only way interstellar travel is remotely possible is through some kind of combination of hibernation systems, which artificially prolongs our life expectancy to hundreds or even thousands of years, and methods of propulsion that can cross some lightyears within that timeframe. I just don't see this option as being practical unless we achieve some miraculous breakthrough of technology.

Maybe there are hundred, even thousands of civilizations throughout the universe, but none of them find it worthwhile to journey to any place aside from the immediate vicinity of their planet.

Hibernation and high sublight transportation are perfectly feasible, but they don't fit in with our current Western profit motive, so no "3. PROFIT". Face it, we're currently on the evolutionary path to Ferengenar.

I am not so certain that it's possible. We know that in interstellar space there is some hydrogen. Now to move from one star to another in any decent amount of time it would require speeds where those same hydrogen atoms could possibly become very dangerous. So it might not entirely be possible for us to do yet. Not to mention that our shielding is not very good.

One of the things we can't find out about exoplanets right now is whether they have magnetic fields strong enough to shield them from solar and cosmic radiation.

? It is our Sun that shields us from 90 % of the cosmic radiation (by yes, its extensive magnetic field), and our atmosphere that block most of the remaining 10 %. Earth's small volume of added magnetic field doesn't do squat against CR in comparison.

If that were true then Venus and Mars would be lovely places to visit.

Our magnetic field protects our atmosphere from energetic rays that flow from the Sun itself. Unlike Mars, Venus likely has a core and geological activity that could create such a field... the problem is, Venus is barely rotating relative to the sun. No rotation = no magnetic field = bombarded by solar rays = runaway greenhouse effect.

*Why* Venus isn't rotating is a good question, but ultimately academic since we're likely no more able to get it spinning than we are able to melt Mars' core and get a magnetic field going there. Still, the fact that there seems to be *two* potentially habitable planets in our system (three if you count Mars - I don't), makes me a little more hopeful that there might be at least one in other solar systems.

Why haven't we found aliens, then? Again, I suspect that interstellar travel and communication are just too hard. Not enough bang for the bucks.

Humans haven't encountered aliens because aliens were disgusted when they saw lots of space garbage orbiting planet Earth. "Aha, nice planet, nevermind it's a third world planet. Just see those metallic garbage floating around."

On a serious note, humans will probably conquer Milky way only when we realise we need more energy and more rare-earth materials due to human greed and the urge to consume more and store more. So greed is a positive trait in this context.An intelligent being will not be interested in Earths resources. More interesting would be energy of stars, similar to that of Sun.

Just provide water(H20) and Sun, and any Type III civilization will be able to convert an inhabitable planet into a habitable one.

Communication with aliens will be difficult. Difficult to disprove that GRB 970228 is not a type of communication from a very advanced civilization. It could be a wireless comm which can be deciphered depending on present wavelenghts on that burst.

I think the premise that a civilization will colonize vast sections of the universe or even a galaxy is incorrect. I don't believe a species that could travel interstellar space would venture clear across a galaxy simply for more real estate. And forget about inter galactic travel. The distances are just too probative.

The universe is unimaginably large. I have no doubt that there are other civilizations out there that have come and gone in the past. And are still out there as well. But would we really be able to detect them clear across the plane of our galaxy? What type of energy output would they have to produce for us to see another civilization hundreds of millions of light years away in a different galaxy? I don't think it's feasible with our current technology. Then add in the time frames involved and it's not hard to understand why it's so hard to find signs of life in the universe.

I will never understand the blindness that always seems to equate "intelligent life" with technology, on an industrial scale even. Maybe this kind of "intelligence" is not only rare but then also much more probable to lead to an early end of a civilization by resource depletion, wars...

So maybe the universe is teeming with intelligent life that is clever enough to get itself organized on a planetary level without wasting resources on any kind of industrial-scale technology (and only this would lead to emissions that we could detect)? Maybe WE are the anomaly?

Right. The universe is 13-14 billion years old. It took about 1 billion years for the first galaxies to form. Then it's going to take multiple generations of star formation in order to create the amount of heavy elements (via supernovae) necessary for rocky planets much less the rare Earth metals that we depend on for our current level of technological development. That drastically cuts down the window for intelligent life to evolve.

Wrong. The oldest planet, with a terrestrial core, is ~ 13 billion years old. (And gas giants are harder to form without metalicity, large cores.) The oldest with pretty much the current element inventory (Sun-like metalicity) is IIRC ~ 12 billion years old, doing the web rounds the other week.

Well, this 13 billion year old planet that you cite (PSR B1620-26 b) orbits a binary pulsar-WD system (unless you're talking about another that I missed). Is it so unlikely that it formed from enriched remnant material that was spewed out during the progenitor star's giant phase? Granted I haven't been actively researching planet formation in a few years, but I was under the impression that the core accretion model needed a metallicity condition in order to be efficient? I'm not saying that planets don't form at relatively low metallicities, only that it's less efficient.

Quote:

By the way, "rare earth" metals, no large E, are among the most common crust elements. They got their name because they are hard to mine out of ore, not because they aren't all over the place.

Oh, right, I stand corrected on the rare Earth metals part. Was a throwaway statement that I placed in at the last minute.

Because the Universe is a Really Big Place and we can't see past our doorstep? Because of the vast distances what we see now is what happened thousands or millions of years ago so we don't really see what is happening now? During the time that the light travels from some place far away to Earth entire civilizations will raise and fall and we won't see that until million years from now.

Fermi Paradox is BS and omits the above: they're there, we just can't see them.

If they are in our galaxy, they aren't millions of light years away from us, they'd be at most 80,000 light years away. If they are in another galaxy, I'd guess that the odds of intergalactic travel are pretty small, and any alien life in other galaxies might as well not be there as far as we're concerned. If your galaxy has hundreds of millions of habitable planets, why travel all the way to another galaxy?

Or maybe we just haven't been listening very long. Or maybe they're too far away. Or maybe they're using a form of communication we can't comprehend yet. Or maybe they're hiding. Or maybe we're the first. Or maybe we're alone. Or maybe they just don't like us. Or maybe... You get the point. All we can do is guess until we have more data.

Please. This hypothesis completely ignores the fact that up until the alien culture would have to deal with a warming planet there should have been countless decades worth of radio transmissions that we could have picked up.

There has to be a first... And in a conversation of wild probabilities, include that possibility. We don't yet understand where life comes from, or even what encompasses life. We don't know if there are creators or not. We don't even know if this is a simulation or not.

How many other civilizations have contemplated the same conundrum over the past 13 billion years? I'm pretty sure we don't really count until we actually figure out a way to survive the death of our planet.

Please. This hypothesis completely ignores the fact that up until the alien culture would have to deal with a warming planet there should have been countless decades worth of radio transmissions that we could have picked up.

We almost always inevitably ignore timescales. Alien civilisations could rise and fall in the blink of the cosmic eye. The chances of any two races enduring for a sufficient amount of (overlapping) time to cross paths with each other is just as much of an issue as any problem with distance or habitability.

Please. This hypothesis completely ignores the fact that up until the alien culture would have to deal with a warming planet there should have been countless decades worth of radio transmissions that we could have picked up.

Try again, this time though leave the politics out of it

Already been addressed, but I will outline the based premise for you: We would be lucky if any of our spurious radio transmissions even made it to the closest star much less the entire galaxy. Basically, all radio signals will be indistinguishable from noise at about a few ly from Earth. So no, the only signals SETI has any hope of finding are intentional high-powered interstellar communications.

Dear David,you do a poor job explaining the Fermi Paradox (as you can tell from the quality of objections in this thread). Actually, the whole premise of the article makes me skeptical whether you understand it yourself. (nice headline-baiting, though).

To make it short: The paradox is alive and kicking. In addition to long-shots like the Zoo-Hypothesis we have two very plausible solutions: (A) We are (almost) alone + super-special (B) our civ is (almost certainly) going to die in the very near future (like all the other civs at this stage).

This view hasn’t changed for decades.

Let me make a number of points on your article:

(ONE) Discovery of habitable planets does NOTHING to increase our probability estimate of alien life. [*] [**] The number of habitable planets is only ONE of the factors in the famous (and meaningless) Drake-Equation. Most of it’s factors are unknown or even unknowable (what fraction of intelligent life builds civilizations, anyone? …Bueller? …Bueller?).

Get it? It doesn’t matter if the number of habitable plants is high. Multiply [High Number] with [High Number]^-1 … Hope you see my point.

[*] I ll ignore the rather unimaginative terra-centrism of assuming only earth-like planets can harbor life.[**] And No – Bayes doesn’t help, because we don’t have an a priori estimate.

(TWO) No idea, who told you that AGW (and it’s counterparts on alien planets) are possible bio-sphere killers. Piece of advice: Never listen to that person again.BTW: Nobody at the IPCC claims that 3C will result from Co2. The reported temp increase is based on papers that postulate a number of *feedback* mechanisms that will result in the 3C warming. Even if we increased Co2 levels 10fold, it alone would not lead to a 3C warming (w/o the postulated feedbacks). Why? Because the relevant spectrum will eventually be 100% opaque (no such thing as 101% opaque) and at this point a higher atmospheric Co2 concentration won’t lead to more warming.

I know, science is hard – and humans are naturally drawn to linear systems (and extrapolations). But if you have have no clue why write about it?

(THREE) Quote from your article: “miraculously moderated climate change”. Yuck. Are you unconsciously going creationist here? In addition to the Fermi Paradox you don’t seem to understand the anthropic principle, neither… Let's leave miracles to the big guy in the sky.

(FOUR) You don’t seem to be aware of the (necessarily decreasing) heating effect of radioactive decay in the earth’s core. Ditto, for leftover heat from earth’s creation. Isn’t this High School level stuff ?!

(FIVE) What’s the deal with the last paragraph? Too many vampire novels?

With all the talk of radio waves being tossed around, I think the best example of why we wouldn't detect radio waves from an alien civilization is pretty simple: if radio waves could travel many light years, don't you think you'd be able to easily pick up all radio-based broadcasts on our own planet? But I can barely pick up my favorite FM radio station once I'm about 50 miles away from the place they broadcast from.

Now, I would think propagation through the Earth is significantly worse than through a vacuum, but to make it 1 light year and not make it through Earth, we're talking about at least 740 million times worse, and that seems pretty high to me. About 110 billion times worse using my radio station anecdote, and I don't think it's passing through much ground at that distance, mostly atmosphere, and the radio waves headed to space are going to pass through quite a bit of atmosphere on their way too.

Maybe those orders of magnitude in difference are reasonable, I don't have much background in the relevant physics. If anyone with more knowledge on the subject cares to correct me, feel free. I understand the inverse square law, but I think this serves as a good practical example if my reasoning is sound.

Well, yes, statistics. Because it is a statistical improbability that life has found a foothold on one, single, solitary rock in one, single, solitary solar system, in one single, solitary galaxy... out of BILLIONS of all of the above.

That's a misuse of statistics. You can't extrapolate anything from a single sample.

Ever wonder why we have radio *towers*? That's right, earth is un-flat. Radio waves have trouble travelling through solid rock (and there is also interference near ground level).Beyond 50 miles you may not have line of sight with the sending antenna, hence bad reception.

As for sending into space: Radio waves are not good at getting through earth's ionosphere, either.Only a fraction of our broadcasts gets through - but some do.

After that - in the vacuum - of space it's pretty smooth sailing. Vaccum is REALLY empty so it won't make much difference whether the signal travels 1 LY or a 1000... So your intuitive reasoning fooled your here.

Where you are right is the problem of the inverse square law - which is the real limit to the aliens ability to pick up our signals (so much sky and so little time...).

PS. As for 740 Mio. times worse...Earth atmosphere at sea level has ballpark 1.245*10^24 Atoms/ cubic-foot - outer space less than one.Like I said: really empty.

Because the Universe is a Really Big Place and we can't see past our doorstep? Because of the vast distances what we see now is what happened thousands or millions of years ago so we don't really see what is happening now? During the time that the light travels from some place far away to Earth entire civilizations will raise and fall and we won't see that until million years from now.

Fermi Paradox is BS and omits the above: they're there, we just can't see them.

By this argument we should be seeing civilisations that arose millions of yrs ago, light from which is finally reaching us. If this is not happening we might have to assume that the universe has only very recentl become hospitable to intelligent life. Not likely in my humble opinion.

Totally agree. Age of our sun, compared to other stars seen in the known universe, is considered younger and that's part of what the Fermi Paradox argues about. If the Earth is atypical, then older stars out there that possibly has a solar system could sustain intelligent life. And just imagining how we reached the peak of our civilization, it was suggested that intelligent life could have solved faster-than-life travel in 10 million years so and that should be enough to colonize other planets. That said, the Earth should have already been visited or colonized by another intelligent life. But that's not the case. Hence, the Great Filter: http://hanson.gmu.edu/greatfilter.html

If a civilization is capable of interstellar travel climate is a non issue for them.

The point of the article is that climate probably is very is important until such time as they develop that capability and that climate change may defeat them before they do.

Hi Likkie,

Let me introduce a hypothesis: The article is flawed.

Dragongoddess statement is true. Especially since even OUR civ is already capable of interstellar probes (Project Orion) AND speaking in terms of the well being of our civilization even the WORST AGW scenarios are a mere nuisance

[Emphasis on civilization as a whole! Obviously outcomes for individual humans could be catastrophic.]

The most obvious explanation for Fermis paradoxon is, that space travel is simply impossible.Let us assume, that our current physics is correct and we do not miss a major insight. Then light speed is indeed the fastest way to travel. Even not light speed itself, but a fraction of it, since we are bodies with a mass.Then, one would need years even to reach the next solar system and including time for acceleration and braking it would be decades of space flight even if all technical problems could be solved.If now not every solar system contains habitable planets, then it is simply impossible to colonize the galaxy.

It is probable in my eyes that humankind will never be able to leave our solar system, no matter how much further advanced it might get technologically. Not because we are luddites but just because we already know the cornerstones of physics.

A) Our radio and TV broadcasts are traveling out at the speed of light

B) The ability to travel to the nearest stars is not delimited by physics but our industrial/energy outputs. Physically possible, just need to colonize the Solar System for resources first.

If a civilization is capable of interstellar travel climate is a non issue for them.

The point of the article is that climate probably is very is important until such time as they develop that capability and that climate change may defeat them before they do.

Hi Likkie,

Let me introduce a hypothesis: The article is flawed.

Dragongoddess statement is true. Especially since even OUR civ is already capable of interstellar probes (Project Orion) AND speaking in terms of the well being of our civilization even the WORST AGW scenarios are a mere nuisance

[Emphasis on civilization as a whole! Obviously outcomes for individual humans could be catastrophic.]

Sigh, does mentioning using the phrase "climate change" send out some form of bat signal?

You've completely misunderstood the article. It's nothing to do with AGW and everything to do with climate change. A planet's climate can vary a lot without intelligent intervention. Except the Earth, of course, whose climate has remained remarkably stable during the 4.5 billion years it took for us to appear. How remarkable this is is one of the questions posed by the article.

Fermi Paradox results from a lots of parameters we don't manage yet: - Empathy: what is intelligent life? How they would consider what is another intelligent life (dudes, they contacted the ants and trees cause their alienthropisms, as humans even today with education don't consider other earthling intelligent life: insects, octopus, birds, orcas, elephants, plants,.. )?- Means to observe them, means they have to travel space (if they can't really go faster than light...no Fermi paradox for sure)- Probabilities that even if there is some intelligent life out there, they are not reaching the Earth every day/century. If last time they visited us, there were only giant pandas, big megalodons and funny chimps. Radio and laser signals need time to reach them, informing them that something is developing there.

nice 'sigh' - would be even nicer if you followed up with something meaningful.The author of the article choose to go on the AGW tangent.

Probably better to worry about your own understanding, first.

Better luck next time.

Huh? Did you even read the article? Where did he go on an AGW tangent? Care to quote? He explicitly states he's not talking about AGW:

Quote:

So why don’t we see advanced civilizations swarming across the Universe? One problem may be climate change. It is not that advanced civilizations always destroy themselves by over-heating their biospheres (although that is a possibility). Instead, because stars become brighter as they age, most planets with an initially life-friendly climate will become uninhabitably hot long before intelligent life emerges.

The universe is a very big place. So big that the vast majority of it is likely empty of advanced civilizations. The Fermi paradox doesn't deny this, indeed, it's always been based on the argument that the universe is so big that we should have seen some advanced aliens since there are so many places they could come from.

Ask yourself how many Gorilla's or Baboons got visits from human beings when we were sparesely populated hunter gathers. Even better ask yourself how many people tried to talk to a baboon or otherwise interact with it.

The Fermi paradox solves itself. We just mastered radio so if we accept the numbers in the Drake equation there should be plenty of civilizations far more advanced than we are. Those advanced civilizations have probably studied enough nearby primitive civilizations to satisfy their curiosity and don't go trying to contact lower life forms.

Moreover, just like the earth there are likely better and worse galactic neighborhoods for high-tech civilizations. In general, the more energetic the environment the more opportunities for a highly advanced civilization to exploit fundamental physics to do computation. It's totally possible that advanced civilizations are all encoded into computations exploiting high energy physics in neutron stars or in the regions around blackholes.

Why would civilizations be interested in some dumb animals in the sticks where energy density isn't even high enough to enable serious computational density.

That's a good point. I have to admit I didn't think of that. Perhaps civilizations don't make enough impact in their systems so that we can detect them unless they're really close? After all, our ways of observing distant planets are still rather primitive. If someone observed our solar system from millions of light years away what would they see?

If they observed it with our level of technology, they 'd only see the sun. And you are right, with our current methods of observation, we wouldn't be able to detect an alien civilization. We'd only be able to detect some form of megastructure, like a Dyson sphere, but that's more like a human thought experiment than an actual thing. Constructs like that might not be a practical or necessary way to utilize solar energy, or there may be better sources of energy than solar out there that we are unaware of that can be harvested with means that we cannot detect. The fact that we do not yet know what 90% of the universe is made of does not bode well as far as our breadth of understanding is concerned.

The universe is a very big place. So big that the vast majority of it is likely empty of advanced civilizations. The Fermi paradox doesn't deny this, indeed, it's always been based on the argument that the universe is so big that we should have seen some advanced aliens since there are so many places they could come from.

Ask yourself how many Gorilla's or Baboons got visits from human beings when we were sparesely populated hunter gathers. Even better ask yourself how many people tried to talk to a baboon or otherwise interact with it.

The Fermi paradox solves itself. We just mastered radio so if we accept the numbers in the Drake equation there should be plenty of civilizations far more advanced than we are. Those advanced civilizations have probably studied enough nearby primitive civilizations to satisfy their curiosity and don't go trying to contact lower life forms.

Moreover, just like the earth there are likely better and worse galactic neighborhoods for high-tech civilizations. In general, the more energetic the environment the more opportunities for a highly advanced civilization to exploit fundamental physics to do computation. It's totally possible that advanced civilizations are all encoded into computations exploiting high energy physics in neutron stars or in the regions around blackholes.

Why would civilizations be interested in some dumb animals in the sticks where energy density isn't even high enough to enable serious computational density.

I'd argue that detection and cataloguing of other complex life forms is something that any advanced civilization would keep doing by devoting a very tiny fraction of its computational power (it really shouldn't be that big of a deal to keep a few ultra high tech detection instruments operational for such a civilization). That's basically biological cartography. You don't just say "Ok screw it, I've had enough" and stop mapping your environment. Contact of course is something different and I would find it natural if they really were not interested in officially communicating with us, in the same way that we are not interested in communicating with a new species of frog in the Amazon forest. We catalogue and move on.

Obviously the estimates made by those scientists ("warp drive within our lifetime a possibility") are probably optimistic, but there are at least some smart people who think it's possible to travel to other star systems ("Alpha Centauri in two weeks").

One other thing to keep in mind in the entire discussion is that even if life developed on some planet, the chance that sentient life develops (as it's usually called in Star Trek ) is probably quite small as well. Contrary to popular belief, it's not certain that sentience is the inevitable outcome of a "survival of the fittest" scenario. In his book The Symbolic Species, Terrence Deacon offers a very specific account, which in itself may or may not be true, but which shows that what lead to sentience in humans may well be a very particular and unlikely set of circumstances. We shouldn't expect this to happen on every planet where life evolves. (In other words, the f_i factor in Drake's Equation may actually be very small indeed.)

Remarkably, biological and geological evolution have generally produced cooling.

Doesn't seem that remarkable to me - biological systems need external energy - it seems unlikely they would evolve to use LESS in the presence of plenty of available energy. Now, geological - maybe it is remarkable.